Generally, the electromagnetic waves (it is hereafter described as a signal) emitted from a satellite or astronomical body pass through the ionosphere and the troposphere, in order to reach on the ground. When a signal passes through the ionosphere and the troposphere, delay of a signal occurs. These delays are called ionosphere delay and troposphere delay, respectively. Therefore, when using this signal as a positioning signal, these ionosphere delay and troposphere delay are one of the sources of a positioning error.
Since the amount of ionosphere delay in the ionosphere changes with frequency, it can calculate the amount of ionosphere delay by receiving the signal of two frequencies. On the other hand, since the amount of troposphere delay in the troposphere changes with temperature, atmospheric pressures, atmospheric steam, etc., it not only always changes with a season or time, but it changes a lot locally at the time of passage of a typhoon or the cold front.
However, the amount of troposphere delay cannot be measured directly. Thus, the amount of troposphere delay is changed according to a weather condition or geographical conditions. Therefore, also in time and in space, the amount of troposphere delay has a large change.
In the positioning of a movable body, in order to correct the amount of troposphere delay, the correction information of the amount of troposphere delay which can be applied to real time at optional points is indispensable. Therefore, generally, by the positioning of the movable body, the amount of zenith troposphere delay is modeled as a function of only altitude, and is used. And in SBAS, the model of the amount of zenith troposphere delay to which the correction of a positioning signal is called a MOPS model is used. This MOPS model is a function of the date, the Latitude and altitude.
The MOPS model is the abbreviation for Minimum Operational Performance Standards for Global Positioning System. And the MOPS model is a function of the amount of zenith troposphere delay defined by the following SBAS agreement document.
“RTCA: Minimum Operational Performance Standerds for Global Positioning System/Wide Area Augmentation System Aorborne Equipment, RTCA/DO-229C, 2001.”
The SBAS is a global positioning system reinforcement system (Satellite Based Augmentation System: describes it as SBAS.) which is a system for making the conventional positioning accuracy improve. This SBAS aims at correcting a satellite orbit, a satellite clock, and the source of a positioning error of ionosphere delay with high precision.
In two or more aeronautical stations installed in the known datum point, distance of the aeronautical station and the navigation satellite measured with the positioning signal from a navigation satellite, the error of the distance obtained from the position information on a navigation satellite and the position information on an aeronautical station is transmitted to a geostationary satellite as correction information, and these correction information is transmitted to the user from the geostationary satellite.
A user receives this correction information. Subsequently, by this correction information, the user corrected the error included in the positioning signal from a satellite, and has improved positioning accuracy.    [Patent documents 1]: JP,2003-114270,A